1. Field
The presently disclosed subject matter relates to semiconductor light-emitting devices in which light emitted from a semiconductor light-emitting chip is wavelength-converted by a wavelength converting material, and more particularly relates to reliable semiconductor light-emitting devices for a vehicle headlight and the like, which can project a mixture light having a substantially uniform color tone in a wide range even when they enlarge the mixture light emitted from a small light-emitting surface in the wide range via optical members such as a reflector, a projector lens, etc.
2. Description of the Related Art
Semiconductor light-emitting devices, in which a part of the light emitted from a semiconductor light-emitting chip is converted into light having a different wavelength by a wavelength converting material and in which the mixture light including the light having the different wavelength mixed with the light emitted directly from the semiconductor light-emitting chip is emitted, have been known as a semiconductor light source for various lighting units. In these conventional cases, the semiconductor light-emitting devices are frequently provided with the wavelength converting layer composed of a resin layer including a phosphor particle on or over the semiconductor light-emitting chip such as an LED chip, etc.
Conventional semiconductor light-emitting devices including such a wavelength converting material are, for example, disclosed in Patent Document No. 1 (Japanese Patent Application Laid Open JP2012-169442) and Patent Document No. 2 (Japanese Patent Application Laid Open JP2012-199411), etc. FIG. 7 is a side cross-sectional view showing a first conventional semiconductor light-emitting device, which is disclosed in Patent Document No. 1.
The conventional semiconductor light-emitting device 60 includes: a base board 69; a semiconductor light-emitting chip 61 including a light-emitting layer 61A, a chip substrate 61B and electrodes 61C located on the light-emitting layer 61A, and mounted on the base board 69; a conductor pattern 67 formed on the base board 69; bonding wires 62 electrically connecting between the electrodes 61C of the semiconductor light-emitting chip 61 and the conductor pattern 67; a transparent layer 64 located over a top surface of the light-emitting layer 61A of the semiconductor light-emitting chip 61, and a bottom surface thereof being smaller than the top surface of the light-emitting layer 61A; a wavelength converting material 63 having a convex side surface 63S disposed between the top surface of the semiconductor light-emitting chip 61 and the bottom surface of the transparent layer 64; a frame 66 located on the base board 69 so as to surround at least the semiconductor light-emitting chip 61, the wavelength converting material 63 and the transparent layer 64; and a reflective material layer 65 disposed between the frame 66 and side surfaces of the chip substrate of the semiconductor light-emitting chip 61 and the transparent layer 64 and the convex side surface 63S of the wavelength converting material 63.
In the first conventional semiconductor light-emitting device 60, when the semiconductor light-emitting chip 61 is a blue LED chip and a yellow phosphor such as yttrium aluminum garnet (YAG) is used as a phosphor for the wavelength converting material 63, the semiconductor light-emitting device 60 may emit a mixture light having a substantially white color tone, which mixes yellow light wavelength-converted by the wavelength converting material 63 with blue light emitted directly from the semiconductor light-emitting chip 61.
In general, when the semiconductor light-emitting devices are used as a light source for a lighting unit such as a vehicle headlight, which controls light emitted from the light-emitting devices using a reflector and/or a projector lens, a light-emitting device having a small light-emitting surface may be required to efficiently control light emitted from the light-emitting device with a small optical structure. Accordingly, the semiconductor light-emitting device 60 can be used as a light source for the lighting unit such as a headlight, because the light-emitting device 60 may emit the mixture light having the substantially white color tone and a high light-emitting intensity from a small light-emitting surface, which is a top surface of the transparent layer 64 that is smaller than the top surface of the light-emitting layer 61A of the semiconductor light-emitting chip 61.
In such a structure, the semiconductor light-emitting device 60 may emit a uniform mixture light having the substantially white color tone from a middle portion of the light-emitting surface, which is the top surface of the transparent layer 64. However, such the structure may tend to emit a mixture light having a little different color tone from the white color tone from a peripheral portion of the light-emitting surface because of various reasons such as optical characteristics, physical characteristics, etc.
A difference between the mixture light having the substantially white color tone emitted from the middle portion of the light-emitting surface and the mixture light having the little different color tone emitted from the peripheral portion may cause a chromatic variability in white color light emitted from the whole light-emitting surface of the light-emitting device 60. Especially, when the white color light emitted from the whole light-emitting surface of the light-emitting device 60 is projected and enlarged by the reflector and/or the projector lens, for example, to form a light distribution pattern of a headlight, the chromatic variability could fail to form a favorable light distribution pattern.
Hence, a second conventional semiconductor light-emitting device, which can reduce the chromatic variability, is disclosed in Patent Document No. 2 by the same inventors as this application. FIGS. 8a, 8b and 8c are, respectively, a top view, and side cross-sectional views taken along lines A-A and B-B shown in FIG. 8a, showing the second conventional semiconductor light-emitting device, which is disclosed in Patent Document No. 2.
The second conventional semiconductor light-emitting device 50 includes: a mounting board 59; a light-emitting diode chip 51 (LED chip 51) including a light-emitting layer 52, a substrate layer 53 and electrodes 55 located on the light-emitting layer 52, and mounted on the mounting board 59; a conductor pattern 56 formed on the mounting board 59; each of bonding wires 57 electrically connecting between a respect one of the electrodes 55 of the LED chip 51 and the conductor pattern 56; a wavelength converting material 54 having a convex side surface covering a top surface of the substrate layer 53 along with a top and side surface of the light-emitting layer 52 of the LED chip 51; and a transparent layer 58 disposed on the wavelength converting material as a light-emitting surface of the device 50 so as to be able to emit a mixture light, which mixes light wavelength-converted by the wavelength converting material 54 with light emitted directly from the LED chip 51.
In this case, when the LED chip 52 is a blue LED chip and a yellow phosphor such as yttrium aluminum garnet (YAG) is used as a phosphor for the wavelength converting material 54, the semiconductor light-emitting device 50 may also emit a mixture light having a substantially white color tone by an additive color mixture of blue light and yellow light. In addition, the semiconductor light-emitting device 50 can reduce the chromatic variability by directly emitting the mixture light (white light) from the convex side surface of the wavelength converting material 54 not through the transparent layer 58 around the peripheral portion of the light-emitting surface (the transparent layer 58), which emits the mixture light having the little different color tone from the white color tone emitted from the middle portion of the light-emitting surface.
FIGS. 9a and 9b are a side view and a front view depicting a measuring method for evaluating a chromatic variability of the second conventional semiconductor light-emitting device 50, which is disclosed in Patent Document No. 2. The semiconductor light-emitting device 50 is mounted on a mounting board 41, and a screen 43 is located 10 meters away from the light-emitting device 50 so that an optical axis of the light-emitting device 50 intersects with the screen 43 at a right angle. Additionally, a projector lens 42 is located in front of the light-emitting device 50 toward the screen 43 so that an optical axis of the projector lens 42 corresponds to the optical axis of the light-emitting device 50 as shown in FIG. 8a. 
When the semiconductor light-emitting device 50 turns on, the mixture light emitted from the light-emitting device 50 is projected and enlarged on the screen 43 as shown in FIG. 8b. In this case, a chromatic value of the middle portion (M) shows white color of (0.332, 0.344), and a chromatic value of the peripheral portion (P) shows white color of (0.338, 0.349), which is a substantially same value as that of the middle portion (M). Accordingly, the conventional semiconductor light-emitting device 50 can emit the mixture light (while light) having a substantially uniformity.
However, when such a structure is used as a light source for a headlight such that is subject to a vibration and the like, such the structure may lack credibility because the bonding wire 57, the wavelength converting material 54 and the transparent layer 58 are exposed from an external air.
The above-referenced Patent Documents are listed below, and are hereby incorporated with their English abstracts in their entireties.    1. Patent Document No. 1: Japanese Patent Application Laid Open JP2012-169442    2. Patent Document No. 2: Japanese Patent Application Laid Open JP2012-199411    3. Patent Document No. 3: U.S. Patent Publication No. US-2014-0014980-A1 (ST3001-0393)    4. Patent Document No. 4: U.S. Patent Publication No. US-2013-0188381-A1 (ST3001-0373)
The presently disclosed subject matter has been devised to consider the above and other problems, features, and characteristics in the conventional art devices. Embodiments of the disclosed subject matter can include reliable semiconductor light-emitting devices that can emit a wavelength converted light having a high uniformity and a high light-emitting efficiency from a small light-emitting surface. The disclosed subject matter can also include the reliable semiconductor light-emitting devices, which emits various color lights including a substantially white color light having a high uniformity and a high light-emitting intensity with a simple structure, and which can be used as a light source for vehicle lamps such as a headlight and the like, general lighting, a street lighting, a show room lighting, a stage lighting, etc.